\frac{1}{1}-\frac{1}{k+1}

\frac{1}{1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

\frac{1}{1\cdot 2}+\frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\frac{1}{4\cdot 5}+\frac{1}{5\cdot 6}+\frac{1}{6\cdot 7}+\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\frac{1}{4\cdot 5}+\frac{1}{5\cdot 6}+\frac{1}{6\cdot 7}+\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3\cdot 4}+\frac{1}{4\cdot 5}+\frac{1}{5\cdot 6}+\frac{1}{6\cdot 7}+\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4\cdot 5}+\frac{1}{5\cdot 6}+\frac{1}{6\cdot 7}+\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5\cdot 6}+\frac{1}{6\cdot 7}+\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6\cdot 7}+\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}{\LARGE +}\cdots+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+{\LARGE \cdots}+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots{\LARGE +}\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k\cdot (k+1)}

\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

\frac{1}{1}-\frac{1} {4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

\frac{1}{1}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

\frac{1}{1}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

\frac{1}{1}-\frac{1}{7}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

\frac{1}{1}+\cdots+\frac{1}{k-1}-\frac{1}{k}+\frac{1}{k}-\frac{1}{k+1}

n = 1 (slider from 1 to 20, step 1)
list1: {t1, t2, t3, t4, t5, t6, t7, t8, t9, ta, tb, tc, td, te, tf, tg, th, ti, tj, tk}
text1 = Element(list1, n)